Ionic liquids have received considerable attention as an alternative electrolyte for rechargeable battery systems. The goal of this investigation is to develop an understanding on the electrodeposition behavior of zinc within ionic liquid electrolytes and determine whether the unique properties of ionic liquids may allow for enhanced cyclability of the zinc electrode for rechargeable battery systems.

Three different analysis techniques are employed for the investigation of the zinc deposition behavior within an imidazolium based ionic liquid electrolyte. First, the electrochemical behavior of the electrodeposition behavior is analyzed by cyclic voltammetry and potential step methods. Second, in-situ atomic force microscopy (AFM) is conducted to investigate the morphological evolution of zinc during electrodeposition. Finally, in-situ ultra-small-angle X-ray scattering (USAXS) is conducted during the electrodeposition of zinc to understand how the electrode surface evolves during electrodeposition and help confirm the results obtained from the in-situ AFM analysis.

The ionic liquid electrolyte chosen for the investigation of zinc electrodeposition is an imidazolium based system consisting of zinc trifluoromethanesulfonate (Zn(OTf)₂) dissolved within 1-butyl-3-methyl-imidazolium trifluoromethanesulfonate (BMIm OTf), and electrodeposition analysis is conducted on a Pt disk electrode. The behavior of Zn/Zn(II) within the ionic liquid electrolyte is analyzed at various deposition overpotentials, Zn(OTf)₂ concentrations, and temperatures.

Three distinct morphological behaviors are observed during the in-situ AFM analysis: growth of boulder like morphology, growth dominated by favorably oriented grains, and the formation of surface instabilities that manifested as agglomerate islands. The electrodeposition growth of Zn dominated by favorably oriented grains obtains a steady state where the surface roughness remained constant despite continued growth. The in-situ USAXS analysis confirms the results observed by the in-situ AFM analysis. In addition, the USAXS data shows that the zinc deposition behavior is hierarchical whereby the main scattering entities exhibited a sub-structure that remains constant in size with continued deposition.

The results of this research indicate that zinc deposition within an ionic liquid electrolyte can obtain a compact and dense morphology. Furthermore, the morphology can evolve under a steady state condition under certain deposition parameters identified by this research. The improved deposition morphology of zinc within ionic liquid electrolytes may help improve the cycling performance of the zinc electrode and help make zinc based rechargeable batteries a viable alternative for energy storage applications.

Rapid trends show a steady decrease in electronic device form factors, which are miniaturizing and flattening, while demonstrating an increase in device functionality, requiring complex and exacting power needs. This movement has motivated a shift in energy storage design and manufacture to accommodate novel and unconventional materials, new device geometries, and non-traditional fabrication methods. A combination of these strategies will lead to a revolution in the way energy storage components are designed, integrated, and utilized in electronic devices.

In this work, we present one possible strategy combining a materials innovation with simple engineering methods to fabricate and integrate batteries directly onto a device. A novel ionic liquid gel electrolyte compatible with zinc-metal oxide battery systems was synthesized. This gel electrolyte properties and its compatibility with the electrodes, current collector materials, packaging, and substrates were investigated.

A simple, low-cost, solution-based printing method for integrating energy storage components directly onto a device is demonstrated with a direct write dispenser printing system. The dispenser printer is able to pattern "inks" into multilayer devices with custom dimensions.

Printed 1 cm2 zinc-metal oxide microbatteries utilizing the ionic liquid gel electrolyte were fabricated and then various device quantities such as its storage capacity, power performance, self-discharge, and other properties were characterized. Prospective applications of this printable battery include flexible electronics and applications that need highly customized integrated or miniature energy storage such as printed circuit boards, permanent power supplies for autonomous wireless sensors, and active RFID tags.

The advent of printed and wearable electronics has generated a renewed interest in the development of new, novel form factors for high-capacity, flexible, rechargeable batteries. This research aims to enable such advancements by characterizing and optimizing the manufacturing processes and component interactions of printed, rechargeable, zinc-based batteries by utilizing an ionic liquid-based gel polymer electrolyte.

The ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIm][OTf]) with zinc trifluoromethanesulfonate (Zn(OTf)2) salt dissolved in it comprises the electrolyte of interest. As a non-aqueous medium, it has been shown to enable rechargeability in zinc-based battery chemistries. When the electrolyte is combined with poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP), a solid, stable, flexible electrolyte is produced. Is is through the lens of this material that the function and characterization of printed, rechargeable batteries comprised of zinc (Zn) and manganese dioxide-based (MnO2) electrodes are investigated.

With the use of this novel electrolyte, additional variables must be taken into account in order to successfully and consistently produce high performance batteries. The printed electrode surface morphology, electrolyte composition, and manufacturing environment play significant roles in affecting the performance of the battery cells and the components within. To characterize these aspects, battery components were produced via stencil printing, dispenser printing, and casting. Their properties were investigated with electrochemical impedance spectroscopy, cyclic voltammetry, laser confocal microscopy, scanning electron microscopy, Karl Fischer titration, contact angle measurements, and cycle life tests.

The gel polymer electrolyte (GPE) was found to poorly wet the rough, wavy surfaces of the printed electrodes. Within features and cavities on the surface, air bubbles were trapped that increased the interfacial impedance and prevented cell cycling. This was overcome by wetting the interfaces with the ionic liquid-based electrolyte prior to cell assembly in order to produce cyclable batteries. With the manufacturing method determined and the surface morphology characterized, several electrolyte and gel polymer electrolyte compositions were investigated. Higher concentrations of Zn(OTf)2 resulted in cells with higher discharge capacities and higher current densities during cyclic voltammetry tests indicating the importance of having adequate charge carriers within the electrolyte. The amount of environmental water absorbed by the electrolyte was also found to be a function of the quantity of dissolved Zn(OTf)2, where more salt resulted in more higher water content. Cell testing and component characterization determined that the presence of some water within the electrolyte was beneficial to enable improved cell discharge capacities. As a result, it was shown that printed, rechargeable, zinc-based batteries can be manufactured successfully in an ambient laboratory environment without strict air quality control.

The optimal component compositions, as determined from the empirical analyses and characterization experiments, enabled the production of 25 cells with 100% yield. These cells exhibited an average discharge capacity of 0.6 mAh/cm^2 with a maximum of 1.0 mAh/cm^2 over many cycles. The cells also successfully powered a commercial, off-the-shelf microcontrol unit to confirm that printed, rechargeable, zinc-based batteries are capable of being deployed with conventional electronics.

The advancements made within this research have successfully produced and characterized printed, rechargeable, zinc-based batteries with an ionic liquid-based gel polymer electrolyte for printed and flexible electronics. The results presented herein will provide a basis with which many printed systems can be better understood and developed, especially for those comprised of multiple layers.

The electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry have been applied simultaneously to characterize electron-beam deposited carbon film electrodes in LiClO4 or LiPF6-containing mixed electrolytes of ethylene carbonate (EC) and dimethyl carbonate (DMC). The structure of the carbon electrode was found to be amorphous/disordered using Raman spectroscopy. Cyclic voltammetry in LiClO4 / EC+DMC demonstrated features typical of Li intercalation/deintercalation into/from the disordered carbon electrode, and EQCM showed a corresponding mass increase/decrease. Contrary to the case of LiClO4 / EC+DMC electrolyte, LiPF6/EC+DMC electrolyte showed no Li deintercalation out of the thin-film carbon electrode. Combined EQCM and spectroscopic ellipsometry data were compared, and the solid electrolyte interphase density after the first cycle in LiClO4 /EC+DMC was estimated to be 1.3 g/cm3.